u-blox LEXI-R422, System Integration Manual

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LEXI-R422 - System integration manual
UBX-23007449 - R02 Design-in Page 48 of 108
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2.3 System functions interfaces
2.3.1 Module PWR_CTRL input
2.3.1.1 Guidelines for PWR_CTRL circuit design
LEXI-R422 PWR_CTRL input is equipped with an internal active pull-up resistor; an external pull-up
resistor is not required and should not be provided.
If connecting the PWR_CTRL input to a push button, the pin will be externally accessible on the
application device. According to EMC/ESD requirements of the application, an additional ESD
protection should be provided close to the accessible point, as described in
Figure 28 and Table 19 .
☞
ESD sensitivity rating of the PWR_CTRL pin is 1 kV (HBM according to JS-001-2017). Higher
protection level can be required if the line is externally accessible on the application board, e.g. if
an accessible push button is directly connected to the pin, and it can be achieved by mounting an
ESD protection (e.g. EPCOS CA05P4S14THSG varistor) close to the accessible point.
An open drain or open collector output is suitable to drive the PWR_CTRL input from an application
processor, as described in Figure 28 .
☞
PWR_CTRL input line should not be driven high, as it may cause start up issues.
LEXI-R422
P15
PWR_CTRL
Push button
ESD
Open
drain
output
Application
processor
LEXI-R422
P15
PWR_CTRL
TP TP
Figure 28: PWR_CTRL application circuits using a push button and an open drain output of an external processor
Reference Description Remarks
ESD CT0402S14AHSG - EPCOS Varistor array for ESD protection
Table 19: Example ESD protection component for the PWR_CTRL application circuit
☞
It is highly recommended to provide direct access to the PWR_CTRL pin on the application board
by means of an accessible test point directly connected to the PWR_CTRL pin, for firmware
upgrade and/or for diagnostic purposes
2.3.1.2 Guidelines for PWR_CTRL layout design
The PWR_CTRL circuit requires careful layout since it is the sensitive input available to switch on and
switch off the LEXI-R422 modules. It is required to ensure that the voltage level is well defined during
operation and no transient noise is coupled on this line, otherwise the module might detect a spurious
power-on request.